The present invention generally relates to cancellation devices for cancelling a temporary stop mode in which the tape travel is temporarily stopped in recording and/or reproducing apparatuses, and more particularly to a cancellation device for a recording and/or reproducing apparatus, designed to automatically cancel a temporary stop mode in which the tape travel is temporarily stopped so as to temporarily stop a recording operation or to carry out a still-picture reproduction, after a predetermined time has elapsed.
A helical scan type magnetic recording and reproducing apparatus for recording and reproducing a video signal, records and reproduces the video signal onto and from tracks which are formed obliquely to the longitudinal direction of a magnetic tape, by use of rotary heads. Generally, in such a recording and reproducing apparatus, the tape travel is temporarily stopped when the mode of the apparatus is set to a still-picture reproduction mode among the reproducing modes. In this still-picture reproduction mode, the rotary heads repeatedly scan over the same track on the tape, so as to obtain a still reproduction picture. In addition, when the mode of the apparatus is set to a so-called pause mode during a recording mode, so as to temporarily stop the recording operation, the rotary heads continues to rotate but the tape travel is temporarily stopped. In this pause mode, the apparatus is in a waiting state and waits for the recording mode to be resumed.
During the temporary stop mode in which the tape travel is temporarily stopped, the rotary heads continue to rotate and repeatedly scan over the same track on the magnetic tape which is stationary. Accordingly, if this temporary stop mode is continued for a long period of time, the magnetic layer on the magnetic tape may become scraped off by the rotary heads. Further, magnetic particles or powder formed as the rotary heads scrape off the magnetic layer of the magnetic tape, may fill the gaps of the rotary heads.
Thus, the conventional recording and reproducing apparatus was designed so that when it is detected that the temporary stop mode such as the still-picture reproduction mode and the pause mode has continued for a predetermined time, the tape tension is reduced. However, if the tape tension is simply reduced, the tape tension cannot be sufficiently reduced around the periphery of the rotary drum which carries the rotary heads due to the static friction between the pole groups of the tape moving system and the tape, and the tape will remain in contact with the rotary heads. In addition, it is impossible to obtain a desired slack in the tape, because of the mechanical returning motion of the tension pole which is provided in the tape moving system for the purpose of detecting the tape tension. The returning motion of this tension pole is toward a direction for applying tension or towards a direction for introducing slack in the tape, according to the designed location of the tension pole. The quantity of the returning motion of the tension pole depends on the diameter of the roll remaining on the reel when the tension is released, the type of cassette, and the like, and this quantity is not constant.
If excessive slack is introduced in the tape, the tape will run off the tape moving path. In such a case, when the mode of the apparatus is thereafter set to a mode in which the original tape tension is applied to the tape, the tape may hit the edge parts of the guide poles and the like and become damaged. On the other hand, if the slack is insufficient, it is impossible to achieve the original object, that is, to prevent the tape from becoming damaged by the contact between the rotary heads and the tape.
Therefore, the slack in the tape must be strictly controlled, however, such control was difficult to carry out in practice because of the returning motion of the tension pole described heretofore.